As a lock for orthodontic treatment, a lock called "ST lock" has been generally known so far. As shown in FIG. 56, this lock has a locking portion formed at an end of a wire "a" (shown as formed at opposite ends of the wire in the drawing). The locking portion includes a bent-down portion "b" formed proximally to a distal end of the wire "a", a horizontal portion "c" extending distally from the bentdown portion "b", a bent-up portion "d" formed at a distal end of the horizontal portion "c", and a short pin "e" and a long pin "f" brazed at position "g" between the bent-down portion "b" and the bent-up portion "d". As shown with respect to one of the locking portions, the short pin "e" and the bent-up portion "d" are inserted respectively into a pipe P1 and a pipe P2 which are fixedly attached to a band B fitted on a molar tooth. The long pin "f" is bent onto and fixed to the top end of the pipe P1. The "ST" lock is comparatively easy to mount in position, but on the other hand the process of fixing the short and long pins to the wire "a" by brazing involves a very troublesome operation in fabricating the device, because the wire "a" is a material having a thickness of less than 1 mm. Another problem with the device is that comparatively fragile brazed portions are liable to become damaged when a strong pull is applied upon the device in use.
As another type of lock, a lock called "lingual lock" is described in Japanese Utility Model Publication No. 4-18572. This device includes lock portions formed adjacent to a distal end of a wire by bending the wire in a hairpin-like fashion at two locations spaced a specified distance. The lock portions are press-fitted respectively into two tubes fixedly provided on a molar tooth band with a specified distance. With this lock, the problem is that high technical skill and precise care are required in the fabrication of the device because the hairpin-like bent portions must be spaced precisely as designed. Another problem is that since the hairpin-like bent portions are inserted into the tubes and held in position merely by frictional force, there is a danger of their slipping off the tube.